The present invention relates to mixed dielectrics of the type manufactured by mixing materials of different kinds and used in dielectric electromagnetic lenses, dielectric antennas and methods of manufacturing the same.
While expanded polystyrol materials and expanded polyurethane materials have heretofore been used as materials for dielectrics used in dielectric electromagnetic lens reflectors and the like, the dielectric constants of these materials are on the order of 2.5 even in their unexpanded conditions and consequently the desired dielectric constants which may be obtained by changing the expansion ratio of these materials will be about 1.9 at the maximum. If the expansion ratio is decreased in an attempt to obtain higher dielectric constants, the material will be expanded nonuniformly thus making it difficult to produce a homogeneous dielectric. With the known dielectric electromagnetic lens reflectors, the dielectric electromagnetic lens section generally comprises a so-called Luneburg lens whose actual manufacture requires the use of a large number of dielectrics of different dielectric constants, and in the case of the Eaton-Lippmann lens which is also used for the dielectric electromagnetic lens reflectors, the lens is so constructed that the dielectric constant is 1 at the surface of the sphere and the dielectric constant is increased toward the center of the sphere where it becomes infinit thus requiring a greater number of dielectrics of different dielectric constants than in the case of the Luneburg lens. Also dielectrics of relatively large dielectric constants have been used in the antennas of the type employing a dielectric. In these applications, it has been the general practice to mix synthetic resin particles, such as expanded polystyrol or polyurethane particles with burnt particles of a higher-dielectric-constant material, such as titanium oxide or lead zirconate and to change the proportions of these materials to thereby produce a dielectric of any desired high dielectric constant, i.e., a mixed dielectric. Typical forms of these prior art mixed dielectrics are shown in FIGS. 1 and 2. The mixed dielectric shown in FIG. 1 is manufactured by mixing expanded particles 1 of a polystyrol material, for example, with burnt particles 2 of titanium oxide or the like in proper proportions and forming the mixture with the addition of a binder, or alternately it is manufactured by mixing crude particles (pre-expanded particles) of a polystyrol material or the like with burnt particles of titanium oxide or the like in proper proportions, subjecting the mixture to a further thermal expansion and then forming the resulting mixture. A disadvantage of the dielectric manufactured in this way is that the expanded particles 1 or crude particles and the burnt particles 2 differ greatly from each other in specific gravity thus making it difficult to uniformly mix them and thereby making it difficult to produce a desired homogenous dielectric, and another disadvantage is that an increased dielectric constant results in a considerable increase in the weight of the resulting dielectric. On the other hand, the mixed dielectric shown in FIG. 2 is manufactured in the following manner, that is, burnt particles of a higher-dielectric-constant material, such as titanium oxide are added, along with an expanding agent, into pre-expanded crude particles of a polystyrol material or the like during the manufacture thereof and then the mixture is thermally expanded and formed. Thus, while this mixed dielectric is advantageous in that any desired dielectric constant can be obtained by suitably determining the amount of burnt particles and the magnitude of expansion ratio and that a homogeneous dielectric can be obtained, it is still disadvantageous in that the operation of mixing a burnt particle into each crude particle presents a manufacturing difficulty and that an increased dielectric constant results in an increase in the weight of the dielectric as in the case of the one shown in FIG. 1.
A further disadvantage of the prior art mixed dielectric is that since the dielectric is produced by mixing a procelain, such as, titanium oxide or lead zirconate with a resin material such as expanded styrol particles, when a considerably high dielectric constant is desired, the amount of such porcelain must be increased considerably in order to obtain the desired dielectric constant, thus increasing the weight of the dielectric. Still another disadvantage is that the increased weight of the dielectric makes the handling of the dielectric lens or antenna more difficult and it also requires the use of mounting means and more rigid construction.